Necessary Proof
by thevirginSTD
Summary: All seems well after Jean and Marco fully consummate their relationship, while Marco is in heat. However, danger awaits the pair as the true consequences of Marco's Titan bite reveal themselves. First alpha/omega, PLEASE give feedback if you can!
1. Chapter 1

Jean paced outside the infirmary, clenching and unclenching his fists. How had he let himself be distracted like that? He'd been following Commander Levi's lead, so intent on impressing his supervisors that he hadn't noticed Marco lagging behind. If Mikasa hadn't reacted fast enough, he could have been split in-half by that Titan's enormous teeth. Jean knew the giant scrape lining his arm and side was a mark of survival. To him, though, it was a mark of his own defeat.

He couldn't help wondering if there was something wrong with him, after all. Where had his alpha instincts been when his omega had been threatened? He saw the way Mikasa reacted if someone so much as stepped too close to Eren. Her eyes would shine, bright and alert, and her nostrils would flare as she leapt to his side or – more often than not – in front of him. Had Jean's senses been so overwhelmed that he didn't notice Marco was in danger? Or was he not a true alpha, after all?

There was really only one way for him to test his alpha status. But he had to make sure Marco was alive first.

The doors to Marco's room spread open and Jean rushed inside. Marco was sitting up in bed, his side wrapped in bandages and the slice on his arm sewn shut.

"You look terrible," Jean said, though he meant to say I'm glad you're okay.

Marco glanced down, chuckling nervously. "It could have been a lot worse."

Jean wanted to apologize, to make up for his inattentiveness, but instead he said, "Be more careful next time, all right?"

Marco nodded and Jean, unsure of what to do, came to sit beside his boyfriend. The bed creaked under his weight, causing Marco's body to shift towards him.

"I'm usually not that careless," Marco said. "It really snuck up on me." He stretched out his arm, revealing the fang-shaped stitches where the Titan had nearly clasped him in its mouth.

Jean swallowed. "I can't help thinking that I might need to be checked, too."

Marco blinked. "What do you mean? You came out unscarred."

"But you didn't," Jean said. "I'm an alpha. Technically, I'm supposed to sense danger to you. Something must be wrong with me, unless…unless I'm not the alpha I thought I was." He glanced at Marco from the corner of his eye. "Technically…we've never tested that theory out."

A blush rose to Marco's cheeks, speckled between his faint freckles. "W-what are you implying, Jean?"

"There's only one way to find out if I'm a true alpha."

The words hung in the air around them, thick as a fog at dawn. For once, Marco held the power.

"Let's try, then," Marco said.

"We don't have to," Jean insisted, rising to pace the room. "You were just injured-"

"-But that's the reason we should, right?" Marco looked up, his face burning as he met Jean's eyes. "After all, if you're not a true alpha…this could happen again, right?"

Jean glanced at the bandages wrapped around Marco's torso, concealing his lean ab muscles. It was a guise, an excuse to test the theory. But as his instincts kicked in, desire flooding through his body at the thought, that no longer seemed to matter. Marco's squirmish stance, his blush and pleading eyes – they sent hot desire running through Jean in a rush, hot and immediate and consuming.

"You can sense it, can't you?" Marco asked.

It was true. Marco's scent filled the room and Jean, open to it, was consumed by it, that omega smell. Caught up in the danger of their battle, he hadn't noticed Marco was in heat.

In a breath, Jean decided to act. "Get on the bed," he said, closing the infirmary door behind them. Marco sat back until his legs were on the sheets, his entire body stretched out and waiting for Jean. He crossed the room to join the omega, slipping on top of him without a second thought.

As their lips met, warm and desperate, Jean was reminded of times they had found themselves in a similar position before. Each time, he had left, separating himself from Marco while the omega was in heat.

But now, at last, he had no reason to deny Marco's needs. There was nothing he wanted more than to satisfy them, than to be the alpha the omega beneath him purred and whined for. He dug his teeth into Marco's neck, marking him as his own. He sucked long and hard, imagining his mark deeper than that of the Titan.

Marco twisted beneath him so his backside faced Jean. On his hands and knees he craned backwards, arching his back to raise his puckering hole. "I need you, Jean," he gasped. "I need you to take me, to mark me as your own…please, Jean, please…I need you inside me."

Jean grew long and hard and the sight of it and gripped Marco's hips, aligning himself with his hole. Marco pressed back, his asshole slurping up Jean as the omega whimpered with need. More immediate and consuming than even the bite of a Titan, Marco pulled Jean in to his hot, tight hole.

Jean, overcome by Marco's scent and his needy pleads, hammered into the omega. The need to take Marco consumed him as he saw the omega bent before him, on his hands and knees, opening himself for Jean to take. With more aggression and force than he knew he had, Jean slammed into Marco's hungry hole, gripping the omega's hips to keep him in place.

Marco clung to the sheets, gasping for breath between the shakes of quickening thrusts. "Please, do it, Jean!" he begged. "Fill me…make me yours…give me your knot."

Now was Jean's chance to prove he was an alpha after the day's mishap. He leaned over Marco, pressing deeper until he swelled and locked inside. As he came, filling the omega, he confirmed his dominance, his alpha-status.


	2. Chapter 2

Jean couldn't believe this. He had knotted with Marco for the first time and it had resulted in a pregnancy. That alone could have been enough for him to handle, but on top of that, their child was going to be part-Titan. It was growing exponentially inside of Marco and, according to Hanji, would grow so large in womb that it would kill Marco.

Jean sat by Marco's bedside, hesitantly reaching out to press his palm to his bulging stomach. Marco shivered a bit to the touch, his eyes fixed on the wall behind Jean.

"Marco, why don't you look at me?" Jean asked. When Marco's only reply was the trembling of his lower lip, Jean clenched his fist. "Dammit, Marco - Look at me!"

Watery eyes turned to Jean. "Jean, I'm a good omega, aren't I?"

Jean blinked. "W-what...?"

"Haven't I done everything a good omega is meant to do?" His voice shook. "I took you and your manly hardness inside my small pucker hole, and now I carry your seed within me. Isn't this what a good omega does? What did I do wrong, that we now have to choose between my life and your offsprings?"

"Marco..." Jean didn't know what to say. Marco had never talked like that, about them being alpha and omega, so openly outside of bed. Although, technically, they were still in a bed...

"Jean, I understand what your decision has to be," Marco said. "I know you care about me, but my job for you is done. My duty to you is now to carry this child to term, to deliver it. At whatever cost to me." Jean opened his mouth to interrupt and Marco spoke faster. "And I know that in your heart, you think you can save us both, or that your love for me will prevail. But your instincts will get the best of you. And your instincts will tell you to save your offspring, that carries your genes, and that I have done all I can for you."

"You think I'm done with you so easily?" Jean snapped, rising from the edge of the bed. "You think I'll be finished just like that?"

Marco nodded solemnly. "Jean..."

"Marco," Jean growled, manly, "An alpha is never finished."

Jean moved to the end of the bed and crawled on. He ripped the sheets off of Marco, tossing them to the side. With firm hands he gripped Marco's ankles and spread his legs apart.

"Jean!" Marco cried. "Hanji and the others will be back any moment now!"

"Don't say other people's names in my bed," Jean growled. He unzipped his pants and Marco whimpered and squealed with surprise. Jean's hardness popped out, firm and thrustful. "You said you've done all you can for me. That's not true, Marco, and I'm going to prove it."

He aligned himself with Marco's begging hole. Maintaining eye-contact over Marco's swollen belly, he shoved himself inside his omega.

"I'll make you take it again, like you did before," Jean grunted, picking up momentum. Marco felt even tighter than before, his hole hot and shy. "I'll make you beg me to fill you again."

"God, yes, Jean!" Marco cried. "Fill me again with your potent seed! Fuck your seed into me! Make me carry your giant babies! Tear me apart with your procreation wand!"

"Fuck, Marco," Jean moaned. He pulled himself out and slammed himself back in, Marco shaking in the bed with each movement. He reached out and ran his hand over Marco's stomach, which continued to grow with each thrust. "Yeah, you like that don't you, you desperate little omega? You like being stuffed by me, even though you're already bursting with my seed. I won't stop, Marco. Not until I'm done."

Marco's stomach was enormous. The omega leaned back, panting from being fucked and pregnant at the same time. "Jean, I...I..."

"Keep taking it," Jean gasped, using more force. He was close to the edge. "I'm going to fill you again. Don't you dare pass out on me before that. I want to hear you cry out as I stuff you with my seed."

Marco broke into a sweat. "I don't think I...can take much more...the baby...it's coming..."

Jean knew he should stop, should make his decision now. But instead, he pressed deeper inside of Marco and held still as he emptied himself into the man. Marco let out a cry before a cold sweat broke across his forehead and he passed out.

Hanji burst into the room and Jean quickly rose to zip his pants off. "Jean, it may be too late!" she cried, rushing to Marco's side. "Why didn't you call sooner?"

"I was busy!" Jean screamed. He was tired of being questioned by others. "I have needs! I am a man. A chief. I have needs!"

As he screamed, Marco's stomach tore open and a human-sized Titan burst out. It leapt onto Jean and sunk its teeth into his neck.

Levi rushed in and he and Hanji restrained the Titan. Jean, clutching his bleeding neck, ran from the room. Outside, Eren and Mikasa rushed by to assist their superiors. Mikasa paused to say, "Your zipper, Jean."

Jean grunted and ran, covered in blood and reeking semen.


	3. Chapter 3

Jean couldn't believe this. He had knotted with Marco for the first time and it had resulted in a pregnancy. That alone could have been enough for him to handle, but on top of that, their child was going to be part-Titan. It was growing exponentially inside of Marco and, according to Hanji, would grow so large in womb that it would kill Marco.

Jean sat by Marco's bedside, hesitantly reaching out to press his palm to his bulging stomach. Marco shivered a bit to the touch, his eyes fixed on the wall behind Jean.

"Marco, why don't you look at me?" Jean asked. When Marco's only reply was the trembling of his lower lip, Jean clenched his fist. "Dammit, Marco - Look at me!"

Watery eyes turned to Jean. "Jean, I'm a good omega, aren't I?"

Jean blinked. "W-what...?"

"Haven't I done everything a good omega is meant to do?" His voice shook. "I took you and your manly hardness inside my small pucker hole, and now I carry your seed within me. Isn't this what a good omega does? What did I do wrong, that we now have to choose between my life and your offsprings?"

"Marco..." Jean didn't know what to say. Marco had never talked like that, about them being alpha and omega, so openly outside of bed. Although, technically, they were still in a bed...

"Jean, I understand what your decision has to be," Marco said. "I know you care about me, but my job for you is done. My duty to you is now to carry this child to term, to deliver it. At whatever cost to me." Jean opened his mouth to interrupt and Marco spoke faster. "And I know that in your heart, you think you can save us both, or that your love for me will prevail. But your instincts will get the best of you. And your instincts will tell you to save your offspring, that carries your genes, and that I have done all I can for you."

"You think I'm done with you so easily?" Jean snapped, rising from the edge of the bed. "You think I'll be finished just like that?"

Marco nodded solemnly. "Jean..."

"Marco," Jean growled, manly, "An alpha is never finished."

Jean moved to the end of the bed and crawled on. He ripped the sheets off of Marco, tossing them to the side. With firm hands he gripped Marco's ankles and spread his legs apart.

"Jean!" Marco cried. "Hanji and the others will be back any moment now!"

"Don't say other people's names in my bed," Jean growled. He unzipped his pants and Marco whimpered and squealed with surprise. Jean's hardness popped out, firm and thrustful. "You said you've done all you can for me. That's not true, Marco, and I'm going to prove it."

He aligned himself with Marco's begging hole. Maintaining eye-contact over Marco's swollen belly, he shoved himself inside his omega.

"I'll make you take it again, like you did before," Jean grunted, picking up momentum. Marco felt even tighter than before, his hole hot and shy. "I'll make you beg me to fill you again."

"God, yes, Jean!" Marco cried. "Fill me again with your potent seed! Fuck your seed into me! Make me carry your giant babies! Tear me apart with your procreation wand!"

"Fuck, Marco," Jean moaned. He pulled himself out and slammed himself back in, Marco shaking in the bed with each movement. He reached out and ran his hand over Marco's stomach, which continued to grow with each thrust. "Yeah, you like that don't you, you desperate little omega? You like being stuffed by me, even though you're already bursting with my seed. I won't stop, Marco. Not until I'm done."

Marco's stomach was enormous. The omega leaned back, panting from being fucked and pregnant at the same time. "Jean, I...I..."

"Keep taking it," Jean gasped, using more force. He was close to the edge. "I'm going to fill you again. Don't you dare pass out on me before that. I want to hear you cry out as I stuff you with my seed."

Marco broke into a sweat. "I don't think I...can take much more...the baby...it's coming..."

Jean knew he should stop, should make his decision now. But instead, he pressed deeper inside of Marco and held still as he emptied himself into the man. Marco let out a cry before a cold sweat broke across his forehead and he passed out.

Hanji burst into the room and Jean quickly rose to zip his pants off. "Jean, it may be too late!" she cried, rushing to Marco's side. "Why didn't you call sooner?"

"I was busy!" Jean screamed. He was tired of being questioned by others. "I have needs! I am a man. A chief. I have needs!"

As he screamed, Marco's stomach tore open and a human-sized Titan burst out. It leapt onto Jean and sunk its teeth into his neck.

Levi rushed in and he and Hanji restrained the Titan. Jean, clutching his bleeding neck, ran from the room. Outside, Eren and Mikasa rushed by to assist their superiors. Mikasa paused to say, "Your zipper, Jean."

Jean grunted and ran, covered in blood and reeking semen.


	4. Chapter 4

A pure anger rustled inside of Jean as he sat on the edge of his hospital bed, thick blood oozing from the wound his son had left on his shoulder. How could this be the end of his relationship with Marco, or his son? He had proven his alpha status, yet felt like he had nothing for it. Perhaps he had made the wrong choice, knotting with Marco directly after his injury.

But if he hadn't, where would he and Marco be now? Sure, Marco wouldn't be dying, and their child wouldn't be a half-breed monster. But Jean would still be doubting his masculinity. The reassurance that he was a true alpha was more than enough to make up for all that was lost.

The smell of thick, soggy heat wafted into his room. Yes, those alpha senses Mikasa had doubted he had - that everyone had doubted - now worked overtime.

He leapt to his feet, crying out, "Marco?"

Instead, Eren appeared in the doorway. Jean's chest fell. "Captain Levi told me to catch you up," he said. "Marco is still in critical condition. They're not...Hanji isn't sure she can..."

Jean clenched his jaw. And his fists. "They're going to let him die."

"Mikasa says they could have saved him," Eren said, quietly, "if we had acted sooner."

"Meaning, if I hadn't taken time to fuck him," Jean growled. "Well, not all of us can be like Mikasa, Eren. Not all of us can suppress our natural and healthy urges. Not all of us can let out fucking omegas crawl around, whining to be fucked, and give them no release."

He stared at Eren who stood, lingering in the doorway, his hip rubbing against the doorframe. Mikasa left him like that, needy and hungry, and never knotted with him. Yet she saw herself as a superior alpha than Jean, who had fucked Marco to the last minute. What kind of logic was that?

I'll show her, Jean thought. Saying what happened to Marco was my fault, being so smug, sending Eren here to talk to me. I'll show her.

Jean unzipped his pants, allowing them to bunch around his ankles. Eren gasped and stepped back, recoiling towards the door. Jean let out a gruff laugh. "Don't play with me, pup," he grunted. "You stink of heat. I know you'd die for cock."

Eren's cheeks flushed and he hesitantly moved towards Jean. "Mikasa is my alpha," he said, his voice a near-whisper. "I can't..."

"Mikasa is no alpha," Jean said. "You want it, don't you, you little omega slut?"

Eren let out an involuntary whine, his eyes fixed on Jean's growing length. He licked his lower lip so it puckered up, glistening and wet.

"Down, boy," Jean hissed. Eren fell to his knees, crawling in front of his hardened cock. Precum dribbled from the top. Jean moved so it dripped onto Eren's face. "You like that, huh?" Eren closed his eyes and opened his mouth, gasping for the cum as it dribbled across his face. "You'd just love to suck me off, wouldn't you? For me to stuff my giant, throbbing manhood down your slutty throat?"

"P-please..." Eren gasped. "I need it, Jean. I need you."

"That's right. You need me to fuck you," Jean grunted, "because that frigid bitch Mikasa won't. Because I'm the real alpha, and I'm going to nail her fucking omega into oblivion."

Jean wanted nothing more to jack off then, to splatter his load across Eren's desperate, whining face. But his revenge needed to be more full than a facial. "Get on the bed, you dirty whore. Crawl." Eren crawled on his hands and knees, cum still dribbling down his face. Jean watched his ass cheeks bob as he moved. "Good boy. Now turn over. I want you to look in my eyes while I fuck you."

Eren turned onto his back, spreading his legs so his desperate hole stared at Jean. Jean positioned himself by it, but didn't enter.

"I need you to say it," Jean said. "Say I'm the real alpha. Say you need me to fuck you because Mikasa isn't alpha enough."

Eren gasped, shaking his head while his eyes watered. Yet he cried out, "You're the real alpha, Jean, and I need you to fuck me! Mikasa won't, and I need you to be the alpha that fucks me!"

"Damn right," Jean grunted, pressing inside. Eren was insanely tight and he had to push harder, calling whimpers and cries from the omega. "Tell me what I am."

"You're a big, strong, alpha," Eren cried.

"And what are you?"

"A slutty little omega whore," Eren sobbed, pulling his legs apart so Jean could enter deeper.

Jean moved in and out, Eren's needy hole slurping him in and out. "I'm the alpha. I'm the man. I'm the chief!" he screamed, his cock hardening inside Eren.

"I need you to fuck me with your powerful manhood!" Eren cried. "I'm nothing without your cock! I can't live without it!"

"Stupid fucking omega whore!" Jean screamed. "You're a shitty trash can for my seed. You'll be useless, used garbage after I'm done with you. Mikasa won't want you. I won't want you. You'll be no one's, nothing!"

"Don't stop!" Eren cried. "I need it! Please!"

"Stupid fucking piece of-" Jean ejaculated, a hot spray of man seed. Eren's stomach swelled immediately and Jean gasped, gripping onto his thighs and pressing himself deeper as he ran out the orgasm. "Don't you dare stop, Jaeger. Look me in the eyes as my seed rips you open."

Eren's eyes watered and he gasped, clinging to the sheets around him. He stared at Jean over his swelling stomach, bearing down on his hard cock.

"Don't you dare look away!" Jean cried as the Titan tore through Eren's stomach. Eren closed his eyes and fell limp beneath Jean.

Jean's power had increased. He laughed, throwing his head back and he continued to ejaculate, creamy spray painting the walls.

"My son," he called to the Titan, "for I can only birth men, true alphas."

Mikasa ran in, hearing the ruckus. "What have you done?" she cried, staring at Eren's limp form and torn abdomen.  
"Your shitty omega," Jean cackled. "Oh, yeah, he begged for it, hard. And I gave it to him until my seed ripped him up!" He was laughing so hard tears spilled down his cheeks.

Mikasa's eyes flashed. "Marco is dead, Jean. Because of you! And now you've killed Eren, too..."

"Fucking useless omegas!" Jean screamed, tears catching in his throat. "They can't do shit. They're weak, fucking disposable pieces of trash!"

Mikasa sprung to life, her eyes yellow, fangs bursting from her mouth as she pounced on Jean. She dug her teeth into his neck and tore out his throat. Blood splattered across the room, mixed with semen over the walls and Eren's cum-stuffed corpse.

Mikasa stepped back, taking in the horror show around her. Jean's corpse, and Eren's. The new Titan child sat atop him, cackling with glee as it swam in its open womb. And Marco was in the next room, too. So much had been lost, and all because of one Titan bite. All because she had been the one to save Marco, not Jean.

For what had caused this misery?

"For he never knew," she said, aloud, "that as trees and stars and rain grow and fall, as the seasons pummel over one another in an endless cycle - as baby birds fall from trees, hoping they'll learn to fly - and men are born and raised by dirt and groan - as the earth churns side by side sun by moon, each day passes, millennium in the heart's of the men of children - for through all of this, he never knew that what makes an alpha, what makes a true, genuine, alpha - was never in the movement of the plates beneath our feet, never in the swift and rough gravel of the Earth, but in the light air of the twilight of the moon at dusk, the breeze that lifts the stray strands of our hairs and whispers in our ears: for tomorrow will come, my child - for tomorrow, we will cum."


End file.
